SLC9C1 and heart failure: We hypothesised that EMPA has a direct cardiac effect; since increases in myocardial intracellular Na+ and Ca2+ concentrations are early hallmarks and drivers of cardiovascular death and heart failure [2–6], we investigated whether EMPA (1) directly reduces intracellular cardiac cytoplasmic Na+ ([Na+]c) and Ca2+ ([Ca2+]c) concentration; (2) affect the (upstream) cardiac Na+/H+ exchanger (NHE); and (3) changes (downstream) mitochondrial Ca2+ concentration ([Ca2+]m).